   Definition 2.6 [1]}
A sequence  \(\left\lbrace \,f_{\,i}\,\right\rbrace _{i \,=\, 1}^{\infty } \,\subseteq \, H\)   is said to be a frame for  \(H\)   if there exist positive constants  \(A,\, B\)   such that
\( A\; \Vert \,f\,\Vert ^{\,2} \,\le \, \;\sum \limits _{i \,=\, 1}^{\infty }\; \left|\ \left<\,f \,,\, f_{\,i} \, \right>\,\right|^{\,2} \,\le \, B \;\Vert \,f\,\Vert ^{\,2}\; \;\forall \; f \,\in \, H.\) 
